This capacitive sensor that operates with a high frequency oscillator was found in Radio Electronics from the 90's. The circuit operates around 300 kHz.
The frequency of this circuit depends on C1 and, for the indicated values, it is 1 kHz. Equivalent...
We found this circuit in an old American documentation. The components are from that period and...
This circuit mimics the trill of a bird. We found it in an American documentation from the 90s. It is...